Methods to enhance pulp bleaching and delignification using an organic sulfide chelating agent

Abstract

A method to enhance brightness in Chemical and Mechanical bleached pulps comprising adding an organic sulfide chelant to the Chemical and Mechanical pulp.

We claim:  
     
       1. In a method for making Chemical pulp comprising the steps of digesting wood chips in the digester to create unbleached pulp and then bleaching the pulp; the improvement comprising treating the pulp with from about 0.002 weight % to about 0.02 weight % of an organic sulfide chelating agent, wherein the unbleached pulp is treated after digestion of thc wood chips and washing of the unbleached pulp and before the unbleached pulp has been bleached, wherein said organic sulfide chelating agent is selected from the group consisting of polymeric dithiocarbamate chelating agents and salts thereof and mixtures thereof and wherein no treatment with organic sulfide chelating agent takes place during digestion of the wood chips and washing of the unbleached pulpy and wherein after thc pulp has been treated with said organic sulfide chelating agent, the pulp is then bleached. 
     
     
       2. In a method for making Chemical pulp comprising the steps of digesting wood chips in the digester to create unbleached pulp and then bleaching the pulp; the improvement comprising treating the pulp with from about 0.002 weight % to about 0.02 weight % of an organic sulfide chelating agent, wherein the unbleached pulp is treated during bleaching, wherein said organic sulfide chelating agent is selected from the group consisting of polymeric dithiocarbamate chelating agents and salts thereof and mixtures thereof and wherein no treatment with organic sulfide chelating agent takes place during digestion of the wood chips and washing of the unbleached pulp. 
     
     
       3. In a method for making Chemical pulp comprising the steps of digesting wood chips in the digester to create unbleached pulp and then bleaching the pulp and subjecting the pulp to pressurized oxygen delignification; the improvement comprising treating the pulp with from about 0.002 weight % to about 0.02 weight % of an organic sulfide chelating agent, wherein the pulp is treated either before or during bleaching and the treated bleached pulp then undergoes pressurized oxygen delignification, wherein said organic sulfide chelating agent is selected from the group consisting of polymeric dithiocarbamate chelating agents and salts thereof and mixtures thereof and wherein no treatment with organic sulfide chelating agent takes place during digestion of the wood chips and washing of the unbleached pulp, and wherein the washed unbleached pulp is subsequently either treated and then bleached or is simultaneously bleached and treated.